Preheat the oven to 350°F (175°C) and grease a muffin tin or line with muffin liners.

In a mixing bowl, whisk together the dry ingredients: flour, sugar, baking powder, salt, and poppy seeds.

In another bowl, mix the wet ingredients: melted butter, buttermilk, eggs, lemon zest, and lemon juice until well combined.

Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

Let the muffins cool in the tin for 5 minutes before transferring to a wire rack to cool completely.